We have cloned and analyzed cDNA sequences derived from a family of genes which encode the classical transplantation antigens. Our findings have led to a better understanding of the structure and function of these cell surface antigens, particularly with regard to the regulation of their expression in both normal and cancer cells. We have studied the expression and function of the human interleukin-2 receptor. Our findings suggest the existence of a secreted interleukin-2 receptor which can bind interleukin-2 efficiently, and may function to regulate the interaction between interleukin-2 and its cell surface receptor. By using DNA- mediated gene transfer, we have demonstrated that the interleukin-2 receptor can function effectively in nonlymphoid cells.